Coating parent bore metal of engine blocks

Abstract

A method of fluxing a cast light-weight metal substrate for thermally adhering sprayed metallic coatings thereto, comprising: (a) preparing the substrate to be clean of grease and oil and to have a uniform and homogeneous surface energy; (b) electrostatically depositing a dry flux powder coating onto such prepared surface; and (c) thermally depositing melted metal onto and across the flux coated surface to further thermally activate the flux if not already activated, for stripping away any substrate oxides and to thermally metallurgically bond the deposited molten metal to the substrate.

We claim: 
     
       1. A method of fluxing a thermally sprayed coating, comprising; (a) preparing a cast metallic substrate surface to be clean of oil and grease while possessing surface oxide;   (b) electrostatically depositing a dry flux powder onto said prepared substrate surface; and   (c) thermally depositing melted metal onto and across said electrostatically fluxed surface to thermally activate said flux for stripping away any substrate oxides and for metallurgically bonding the sprayed metal as a coating to the cast metallic substrate.   
     
     
       2. The method as in claim 1 in which the particle size distributions of the dry flux powder applied in step (b) is in the range of 5-100 micrometers. 
     
     
       3. The method as in claim 1, in which step (b) is carried out to electrostatically spray the dry flux powder at a flow pressure of about 2.5 psi (atomizing pressure of 3 psi) accompanied by an exit charge of 1-50 Tesla. 
     
     
       4. The method as in claim 1, in which said thermally deposited metal in step (c) is comprised of a bonding metal selected from the group of nickel-aluminum, aluminum-bronze, and silicon bronze. 
     
     
       5. The method as in claim 1, in which said thermal deposition is carried out by the use of wire arc, high velocity oxy-fuel, or powder plasma thermal spraying to provide superheated metal droplets at a temperature in excess of 1000° C. 
     
     
       6. The method as in claim 5, in which said wire arc spraying is carried out utilizing a spray gun having voltage of 80-220 volts and a current of 60-100 amps. 
     
     
       7. A method of coating adjacent cylinder bore surfaces of a cast aluminum engine block, the surfaces having a bridge wall separating the bore surfaces and having a preconditioned surface with a roughness of less than 50 microns Ra, comprising: (a) washing said surfaces with an aqueous solution of non-etching alkaline cleaning agent comprising borate, carboxylic acid and sodium glucoanate, said agent being effective to increase and make homogeneous the surface energy of said preconditioned surface,   (b) after drying said surfaces, electro-statically applying a dry dehumidified brazing flux that clings to said washed surfaces in a uniform coating thickness of 10 micrometers,   (c) thermally spraying said adjacent bore surfaces at the same time with a bonding metal to simultaneously (i) thermally activate said electrostatically deposited dry flux to strip said surfaces of oxides, and (ii) metallurgically adhere said bonding metal to the stripped surfaces,   (d) thermally spraying a top metal coat over said bonding metal in each bore to metallurgically adhere thereto, said thermal spraying utilizing atomizing air that is pumped through said bores to cool said engine block and avoid distortion causing engine block heating at the bridge walls between said adjacent bores, and   (e) removing a portion of said top metal coat to finish said coated surface to a roughness of 0.1-0.4 micrometers Ra.   
     
     
       8. The method as in claim 7 in which, step (a) is carried out in stages, using said solution pressurized sequentially at about 20-100 psi, 1000 psi, and 20-100 psi. 
     
     
       9. The method as in claim 7, in which the deposited thickness of said bonding metal is in the range of 30-70 microns, and said bonding metal is applied by thermal guns, each rotated about its own axis, said guns being synchronized to rotate in the same direction with said axes being parallel. 
     
     
       10. The method as in claim 7, in which said top metal is selected from the group consisting of low carbon steel, low alloy steels, 3000 series stainless steel, 400 series stainless steel and, said thermal spraying for the top coat being carried out with an excess of oxygen in the propellant gas to oxidize a portion of said thermally sprayed top metal to FeO.